"Severely Reduced DLCO"

I had a recent increase in need for oxygen therapy. My lung doctor had me do some blood tests, an Xray, an ECHO, a Pulmonary Function Test and a CT Angiogram. This is what he reported findng:

"Dr. XXXXs interpretation is: PFT's show mild COPD with a severely reduced DLCO (refers to the transfer of CO2)."

My question is would the severely reduced DLCO be the cause of my increase in Oxygen? As far as I can find DLCO is the transfer of carbon dioxide out of the lungs by the alveoli. My 'mild' copd feels 10 times worse than it was previously. Thanks